M1 Lec 3 Flashcards
what is membrane potential due to
due to unequal concentrations of each diffusible ion inside and outside of the cell
how do cations and anions move with the electrical gradient?
cations: move extracellular to intracellular
anions: move intracellular to extracellular
what is the goldman equation used for
- used to calculate the membrane potential of a neuron or cell, taking into account the concentrations of multiple ions across the membrane and their respective permeabilities.
- only if membrane voltage isnt changing
what did hodgkin and huxley do
pioneered studies with the squid giant axon
* developed ionic hypothesis of axon potentials.
* discovered that selective permeability changes during AP
* identified voltage dependent ion channels and Na influx/ K efflux
purpose of voltage clamp technique + how it is done
purpose: control the membrane potential and measure the electrical current flowing across the cell membrane
how do: voltage is clamped and and current is injected/withdrawn from axon. then they measure current in response to stimulus
action potential characteristics
- Property of all excitable cells
- Brief, regenerative change in
membrane potential - Travels along the axon
- All-or-none
- Triggered when membrane
potential reaches a threshold
what are the action potential stage values for:
* threshold:
* resting potential:
* peak of AP:
* membrane hyperpolarization:
* equilibrium potential of K:
* equilibrium potential of Na:
- threshold: -50mV
- resting potential: -70mV
- peak of AP: +30mV
- membrane hyperpolarization: -80mV
- equilibrium potential of K: -90mV
- equilibrium potential of Na: +60mV
what are graded potentials and where come from
small changes in resting membrane potential of neuron
* come from subthreshold stimulus. they travel down axon but degrade before reaching end
graded membrane potentials change from resting potential. what 2 forms can it occur in?
- EPSP: excitatory postsynaptic potential
- IPSP: inhibitory postsynaptic potential
how does the dendrite relate to epsp
Dendrites receive excitatory signals that generate EPSPs, moving the membrane potential closer to the threshold for firing.
how does the cell body relate to psp
The central part of the neuron that integrates incoming signals from the dendrites.
The cell body acts like a calculator, summing up EPSPs (excitatory signals) and IPSPs (inhibitory signals).
If the combined signals reach a certain threshold, the neuron will trigger an action potential. The cell body integrates all inputs (excitatory and inhibitory) to determine whether the neuron should fire.
how does the axon hillock relate to the trigger zone
The axon hillock is where the decision to fire an action potential is made. If the summed signals (from the dendrites and cell body) exceed the threshold potential, an action potential is initiated here.
what does initiating the action potential rely on?
relies on summation of postsynaptic potentials
* Spatial and temporal summation are mechanisms by which a neuron integrates multiple postsynaptic potentials (PSPs) to determine whether an action potential (AP) will be triggered at the axon hillock.
what is spatial summation
Spatial summation occurs when multiple synaptic inputs (EPSPs and/or IPSPs) from different locations on the neuron (usually on the dendrites or cell body) combine to influence the membrane potential at the axon hillock at the same time
what is temporal summation
Temporal summation occurs when a single presynaptic neuron fires rapidly in succession, causing multiple postsynaptic potentials to overlap in time and sum together.
at rest, is the membrane potential closer k or na
The resting membrane potential (~-70 mV) is closer to EK (-90 mV) because the membrane is much more permeable to K⁺ at rest. Na⁺ and Cl⁻ have smaller effects due to their lower permeabilities.
during action potential, is the membrane potential closer to k or na
During depolarization and at the peak of the action potential, the membrane potential is closer to Na due to the high permeability to Na⁺.
- Voltage-gated Na⁺ channels open rapidly in response to a stimulus that reaches the threshold (~-55 mV).
Na⁺ rushes into the cell, increasing the intracellular Na⁺ concentration.
what could cause a decreased AP amplitude? what could cause an elongated AP duration?
- decreased extraceullar Na concentration (The action potential’s depolarization phase heavily relies on Na⁺ ions rushing into the cell. If there’s less extracellular Na⁺, the driving force for Na⁺ influx is reduced, leading to a smaller change in membrane potential during depolarization.)
- less Na means slower depolarization which means this alters the timing of subsequent events, such as the opening of voltage-gated K⁺ channels for repolarization, making the overall AP duration longer.
what are the phases of action potential
depolarization, repolarization, hyperpolarization, repolarization
what are the three sodium channel states? explain them
closed open inactivated
what are the 2 forms of a refractory period
- absolute: no AP can be generated, regardless of stimulus amplitude being provided
* It lasts from the initiation of the action potential until the Na channels reset to their closed (but activatable) state. - Relative: AP can be generated in
response to large amplitude stimulus being larger than previously necessary
what is the length constant equation used for? whats the equation?
The length constant (λ) is a measure of how far an electrical signal (such as a change in membrane potential) can travel along a neuron before it diminishes significantly due to passive conduction (naturally moving down axon).
length constant
What does a larger λ mean? How to achieve larger λ?
Larger λ means the signal can travel farther along the axon without degrading.
- High Membrane Resistance (Rm) - means less current leakage through the membrane. Myelination increases Rm bc it insulates axon and doesnt let signal decay.
- Low Internal Resistance (Ri) - means less resistance to current flow within the axon. achieved by a larger axon diameter. larger diameters = more space for the current to flow and less resistance as the signal travels through the axon
- High Axon Diameter (Geometry) - A larger axon diameter decreases Ri, which lowers internal resistance and enables more efficient current flow through the axon. With low Ri, the signal faces less opposition, allowing it to travel farther and faster
what is action potential transduction
refers to the process by which a neuron converts a stimulus (chemical, mechanical, or electrical) into an action potential and then propagates that action potential along its axon to communicate with other cells
how can you speed up action potential transduction
- Increasing membrane resistance makes it harder for ions to leak through the membrane
- Decreasing longitudinal resistance makes it easier for ions to flow along the axon, increasing the speed of signal transmission.
- Increase fiber diameter
- Wrapping axons: myelination
how does myelination speed up the signal?
- it provides insulation around the axon
- it creates saltatory conduction which allows signals to jump and move faster
- it increases resistance and keeps the current traveling forward along the axon, rather than dissipating (less current leaks out)
ex of a myelination disorder (demyelinating diseases)
* how to diagnose it
multiple sclerosis:
* diagnose with an electrode placed on the skin to send a signal and see the AP conduction velocity (bc myelinated will be fast)
